A problem which frequently arises within an I. F. mixer stage of a microwave signal transmission system is the degree of undesirable leakage of the local oscillator signal through the mixer. This problem is especially paramount in present day technology where bandwidth expansion is desired; yet, because of communication system restraints, such as modem design, the frequencies employed limit the degree of refinement for elimination of undesirable signals in systems heretofore developed.
Attempts to remove the local oscillator signal at the output of a mixer have included the use of shorting stubs connected between the center lead of the usual 50 ohm mixer output cable and ground. Unfortunately, the Q.sub.u of such tuning stubs is on an order of 300, so that the maximum degree of attenuation of the local oscillator signal has been 10-15dB.
Another problem in such systems has been the reduction in the size or volume of the radio hardware, a problem which is significantly acute when such systems are employed in an airborne environment. Of course, it goes without saying that as the degree of integration of the radio components is increased, interconnection between components can be shortened and losses throughout the system are reduced.